370 



Special Reports 



short brass tubes, one of them shown in Figures A and B, close the holes, except when, at 

 will, one of them is replaced by a copper plug, as in Figure B, to increase the damping; or 

 when the other is replaced by a plane glass mirror, carried normal to its axis by a longer 

 brass tube, to assist in adjusting the telescope; or during alignment tests with the 

 devices shown in Figure C and at the bottom of Figures A and B. An axial (vertical) hole 

 6 mm. in diameter, flaring at the ends, passes through the upper part of the box to admit 

 the suspension. A second horizontal cylindrical hole 3 mm. in diameter passes through the 

 box with its axis intersecting those of the other holes at right angles. Its outer ends are 

 closed by glass windows and its object is to permit sighting along the axis of the magnet. 



The magnets are circular discs of steel polished on both sides, which serve as mirrors, 

 and magnetized in an intense field directed along a diameter. Two magnets have been 

 used. One, made in the instrument shop by Mr. Steiner, is a disc of tungsten steel 20 mm. 

 in diameter and less than 1 mm. thick, provided with small holes near opposite ends of 

 the same diameter normal to the magnetic axis, so that the magnet can be suspended from 

 either end of this diameter in order to determine the angle between the face of the mirror 

 and the magnetic axis. This angle for the face used is about 6'. 



The other magnet is one of the gages 20 mm. in diameter and 1 mm. thick made from 

 chrome steel and polished on both sides by the Bureau of Standards, to which we are 

 indebted for it. The surfaces are flat within a fraction of a wave length of sodium light, 

 and they are parallel within about 1". The angle between the surfaces of the magnet 

 and its magnetic axis is less than 2'. This magnet was not pierced with holes like the 

 other, but was provided with a small closely fitting saddle of brass, illustrated in Figure 

 11, by which it can readily be suspended with the magnetic axis in any altitude. The 

 altitude can be altered at will by simply slipping the saddle along the periphery of the 

 magnet, care being taken to push it in radially at the same time. 



The torsion tube, head, and rod are similar to those 

 on the C. I. W. magnetometers, except that the rod ends 

 below in a small vertical ring for attaching the suspen- 

 sion. A flange at the bottom of the tube is screwed to 

 the top of the copper box, proper arrangements being 

 made for automatic centering. The rod is provided 

 with rack-and-pinion vertical adjustment. The head is 

 provided with a clamp, and is divided into intervals 

 of 10. 



Suspensions of single silk fiber, Wollaston wire, and 

 fine phosphor-bronze strip have been used. They may 



vary from about 18.5 cm. to about 26.5 cm. in length. The bronze strip is especially 

 satisfactory. In addition to other advantages, a metallic suspension has the advantage 

 over silk and quartz of eliminating possible troubles from electrification. Small right- 

 angled geometric hooks are soldered to the ends of the metallic suspensions for holding 

 the magnet and for attachment to the torsion rod. The torsional constant is far too 

 small to be troublesome with any of the suspensions and magnets used. 



The magnetometer box is screwed on to the top of a brass piece A, Figure C, whose 

 central portion B is a circular cylinder and carries the arm holding the telescope and 

 scale. The lowest part L of A is also cylindrical and coaxial with B, but of smaller 

 diameter. L projects through and is screwed to a circular flange C, which fits centrally 

 over a similar flange D forming the top of the brass support BE. The cylinder L just fits a 

 central hole in the top of BE. The two flanges are clamped together with four screws, 

 circular slots in the upper one permitting a little motion in azimuth for adjustment. The 

 support BE is bolted centrally to the saddle F, which carries the marble core on which the 

 coils are wound. The upper portion of this saddle was turned with a fly cutter to the 



-SADDLE. 



Fig. 11. Magnet-Mirror Holder. 



